Researchers from Australia and New Zealand have completed a high tech search for chemicals that can turn ordinary beer into extraordinary beer. It’s all about the hops.

For years, scientists have been trying to identify the chemicals that give the best beers a noble hop aroma. Using sophisticated lab equipment, three researchers have identified several chemicals that may be responsible for a spicy scent. This is no small task since hops contain as many as a thousand different smelly chemicals and the ones that are most abundant are not responsible for the characteristic aroma. Some chemicals smell much stronger than others. The most potent chemicals are often responsible for the finer points of an aroma even if they are only present at very low levels.

Terpenes are a class of chemicals that are often responsible for the unique scent of food, perfume, and beverages. In 2002, other researchers showed that adding a tiny amount of a particular terpene to a very bland beer made it smell fantastic, but not quite as complex as a premium brew.

To identify more chemicals that give hops a spicy character, the chemists hooked two people up to a machine called a gas chromatograph. That machine would separate out every single chemical in an essential oil extracted from high quality hops — allowing the evaluators to smell each chemical one by one. That’s right, they lean over a tabletop machine while it delivers odors directly to their nose through a long, straight tube. The same technique, gas chromatography-olfactometry, has been used to study the aroma of wine, coffee, and even manure.

Both of the assessors described each scent as it was emitted from the machine over a 25-minute period. The chemists would repeat each experiment with lesser and lesser amounts of the pungent oil until no further scents could be detected.

In order to verify the identity of each chemical, the researchers used two-dimensional gas chromatography mass spectrometry. In other words, they used a machine that separates out each individual chemical from the hops in a two-step process, and then weighs the individual molecules to identify them.

When the test results came in, five chemicals stood out from the others. All of them are terpenes. Geraniol, which is named after geranium flowers and obviously has a floral scent. Linalool, has a floral and spicy scent. It is also found in mint, cinnamon, and rosewood. Eugeneol has a spicy, clove-like aroma. Beta-ionone has a complex woody and fruity scent. Caryophyllene is found in black pepper.

The scientists from the University of Otago and RMIT University reported their findings in the Journal of Agricultural and Food Chemistry. They dedicated their research paper to the late Professor Jean-Pierre Dufour, who began this elaborate study of beer and spent his life as a passionate flavor scientist and brewmaster. I can imagine that any man with such credentials will be greatly missed. We should all raise a glass in his honor.

Photo Credit: Dr. Lingshuang Cai and Jacek Koziel at Iowa State University

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